COCKERELL : MOLLUSCAN FAUNA OF COLORADO. 6 1 



Polygyra, &c. being wholly unrepresented. Cochlicopa lubrica 

 occurs locally, and seems less variable than in Europe. Pupa 

 (including Vertigo) is well represented, but the group Leucochila 

 is rare. Succinea is frequent. Among freshwater species four 

 species of operculata are on record, but they must be very 

 scarce ; I never met with any of them. Limnoea has several 

 species of the Lhrinophysa group. Physa is fairly numerous, 

 but Pla7iorbis is poorly represented. Ancylus, Sphcerium, and 

 Pisidhwi occur in the mountains, but Unio and Anodonta are 

 only found in the north-east corner, almost in Nebraska. 



Districts. — Colorado presents very varying conditions at 

 altitudes from 3,450 to 14,480 feet. Roughly, it may be 

 divided into the eastern plains, the central mountain region, 

 and the lower western portion. For more detailed work I have 

 divided it into seventy-eight counties and vice-counties, which 

 fall under nine heads, according to the great river-basins, as 

 follows : — 



Platte.— "YMva division is characterised by several species, found 

 in Lodge Pole Creek, in Logan County, by Mr. Chas. T. 

 Simpson, and at present known to occur nowhere else in 

 the state, viz : — Linmcea modicella Lea, Physa virgata 

 Gould, Planorbis bicarmatus Say, Unio occidens Lea, 

 Anodonta ferrusaciana Lea, and A. plana Lea. All but 

 one of these are now recorded for Colorado for the first 

 time.* 



* Mr. C. T. Simpson also found the following species in the Platte 

 district in S.W. Nebraska, quite close to Colorado ; they are not yet known 

 for our state, but may be looked for in its N.E. portion : — Limncea 

 biilinidides Lea, Physa gyrina Say, Planorbis exaaitus Say, P. armigerus 

 Say, Pupa fallax Say, P. armifera Say, P. contrada Say, Zonites minus- 

 culus Binn,, and young shells of what are probably Unio gracilis Barnes. 



